In charged particle beam systems a target surface may be exposed to one or more charged particle beams directed to and focused on the surface with high accuracy.
In charged particle beam lithography systems, small structures may be formed with high accuracy and reliability. In charged particle multiple beam lithography the pattern formed on the surface is determined by the position where each individual beam interacts with the resist on the surface. In other charged particle beam exposure systems, such as electron microscopes, samples may be analyzed based on the interaction of the charged particles with the sample. Therefore, compliance of the beams reaching the surface with specified beam properties, such as beam position and intensity, is of high importance.
The accuracy and reliability of charged particle beam systems is negatively influenced by contamination. Charged particle beam systems comprise charged particle optical elements for projecting one or more beams of charged particles onto the target surface. An important contribution to contamination in charged particle beam systems is accumulation of deposits of contaminants on surfaces, such as surfaces of the charged particle optical components.
In charged particle beam systems, such as electron microscopes, e.g. scanning electron microscopes, and charge particle lithography systems, the charged particles may interact with residual gases, or contaminants, e.g. hydrocarbons, present in the system. Such contaminants may arise from outgassing from components within the system and/or from the target to be exposed. The interaction between charged particle beams and contaminants may cause Electron Beam Induced Deposition (EBID) or Ion Beam Induced Deposition (IBID) on surfaces of the charged particle optical elements. Contamination layers, formed by EBID or IBID, may perturb the functioning of these elements, and hence negatively influence projection of charged particles on the target surface. Removal of contamination, or prevention of contamination growth, in particular in areas with relatively high hydrocarbon partial pressures and relatively high beam current densities, is therefore highly desirable.
A method for removing contamination is described in US 2015/028223 A1, also by the applicant. US 2015/028223 A1 describes an arrangement and a method for transporting radicals, for example for removal of contaminant deposits. The arrangement includes a plasma generator and a guiding body. The plasma generator includes a chamber in which plasma may be formed. The chamber has an inlet for receiving an input gas, and one or more outlets for removal of plasma and/or radicals created therein. The guiding body is arranged for guiding radicals formed in the plasma towards an area or volume at which contaminant deposition is to be removed. Further a charged particle lithography system comprising such arrangement is described.
Although the method and arrangement described in the document cited above enable cleaning within charged particle lithography systems, the efficiency of the cleaning, in particular the rate of removal of deposits from surfaces, is observed to be limited. It is an object of the present invention to provide a method and a system which reduce the contamination in charged particle beam systems and/or increase the cleaning efficiency in charged particle beam systems.